Duplex printing is a desirable feature in printing systems. The advantages of duplex printing include reducing the amount of paper required as compared to one-side (simplex) printing, and generating print sets with layouts resembling that of professionally printed books. Modern duplex printing is typically accomplished by using one of two types of duplex system employed in printing systems, such as inkjet printers. The two types of duplex systems are back and front duplex systems as shown respectively in FIGS. 1 and 2.
FIG. 1 shows a prior art back duplex system 100 for an inkjet printer. The back duplex system 100 includes a duplex module 102, a linefeed roller assembly 104, and a printhead 106. The general operation of the back duplex system 100 is such that a media sheet 112, such as a printing paper, is fed via a media path entry 110 and received by the linefeed roller assembly 104. The linefeed roller assembly 104 subsequently feeds the media sheet 112 to the printhead 106 for printing on a first side of the media sheet 112. Once printing on the first side of the media sheet is completed, the linefeed roller assembly 104 rolls the media sheet 112 in the reverse direction into a duplex media path entry 114 of the duplex module 102. The media sheet 112 is directed through the duplex media path 116 in the duplex module 102 by two rollers 120 and 122 and back to the linefeed roller assembly 104 via a duplex media path exit 118. The linefeed roller assembly 104 then forwards the media sheet 112 to the printhead 106 for printing on a second side of the media sheet 112.
Although the back duplex module 102 may be installed only when duplex printing is required, the duplex system 100 suffers from not being able to print all the way to the trailing edge 124 of the media sheet 112. The portion of the unprintable area on the media sheet is commonly referred to as “bottom of form” 108 as shown in FIG. 1. The bottom of form 108 margin, typically between 10 to 13 millimeters, is defined by the distance between the trailing edge 124 of the media sheet 118 and the first array of nozzles (not shown) of the printhead 106.
The front duplex system has a duplex module typically housed inside the base of the printer. Thus, the overall size or form factor of the printer remains the same even when the duplex module is removed. The front duplex system overcomes the bottom of form limitation but suffers from large form factor which consumes valuable table space as described herein with reference to FIG. 2. FIG. 2 shows a prior art front duplex system 200 for an inkjet printer. The front duplex system 200 includes a duplex module 202, a linefeed roller assembly 204, a printhead 206, and an output roller assembly 208. A media sheet 212 is fed via a media path entry 210 and received by the linefeed roller assembly 204. The linefeed roller assembly 204 subsequently feeds the media sheet 212 to the printhead 206 for printing on a first side of the media sheet 212.
As the printhead 206 prints, the media sheet 212 is progressively advanced forward and eventually received by the output roller assembly 208. Once printing on the first side of the media sheet 212 is completed, the output roller assembly 208 further advances the media sheet 212 forward until the trailing edge 218 of the media sheet 212 reaches the duplex media path entry 214 area. The output roller assembly 208 then reverses the rolling direction and rolls the media sheet 212 into the duplex media path entry 214. The media sheet 212 is advanced along a duplex media path 216 to the linefeed roller assembly 204 where the media sheet 212 is received and subsequently fed to the printhead 206 for printing on a second side of the media sheet 212.
In the front duplex system 200, the transmission (i.e. the set of gears and belts that drives the rollers) of the output roller assembly 208 is coupled to the transmission of the linefeed roller assembly 204 in order to maintain media sheet 212 feeding accuracy.
Thus, during duplexing (i.e. the process of flipping the media sheet), the trailing edge, which is the leading edge 220 during duplexing, of the media sheet 212 must leaves the output roller assembly 208 before the media sheet 212 is further advanced along the duplex media path by a transfer roller assembly 222 to the linefeed roller assembly 204. This is so because the turning direction of the rollers of the two roller assemblies 204 and 208 are in opposite directions to each other.
This requirement causes the front duplex system 200 to have a large form factor. The form factor is dependent on the size of the media sheet the printer is designed to accommodate. For example, if the media sheet is of A4 size, then the reverse duplex media path length (i.e. the duplex media path entry 214 and the duplex media path 216) between the linefeed roller assembly 204 and the output roller assembly 208 must be longer than the length of the A4 size media sheet. However, if the transmissions of the linefeed roller assembly 204 and output roller assembly 208 can be decoupled, the form factor can be reduced and is only limited by the loop of the media sheet path starting and ending at the output roller assembly 208. Thus, the form factor of the printer of the decoupled transmissions of the linefeed roller assembly 204 and output roller assembly 208 is smaller but still has substantial impact to the base printer size. Further, decoupling the transmissions of the two roller assemblies 204 and 208 is difficult and may be costly.
Therefore, there is clearly a need to provide a duplex system for an inkjet printer that addresses the above-outlined shortcomings of existing duplex systems.